Prior art charge pump circuits have been provided on a semiconductor chip to generate a higher voltage using an on-chip power supply voltage. Most of such conventional charge pump circuits utilizes a switching method of high frequency oscillation. Such a charge pump circuit is illustrated in FIG. 1.
As shown in FIG. 1, the above charge pump circuit has a charge pumping capacitor CP, an oscillation circuit 10 connected between an on-chip voltage source Vcc and a ground. Circuit 10 pumps electric charge out of the capacitor at a rate dependent upon the oscillation frequency. A power supply circuit 20 generates another voltage in response to voltage levels of an input signal Vin to always maintain a constant voltage at a connection point P1 between the capacitor CP and the output of the power supply part 20. A MOSFET (metal oxide field effect transistor) drives a load circuit 50 and a constant current source 30 supplys a constant current to a control terminal (i.e., a gate terminal) of the MOSFET.
The oscillation circuit 10 has two switching elements 12 and 13 which are operated complementary to one another. If the switching element 12 is switched on and switching element 13 is off, the on-chip voltage is applied through the switching element 12 to the capacitor CP thus charging the capacitor CP. If not, i.e., when the switching element 13 is switched on and switching element 12 is off, the capacitor CP is discharged through the switching element 13 to ground. When the on-chip voltage is applied through switching element 12 to the capacitor CP at the point P1, a voltage of about Vcc+12 V is maintained. This is because a voltage of 12 V is applied via the MOSFET 21 to the point P1 by means of the MOSFET 21 to be activated in response to the input signal V1.
As described above, a conventional charge pump circuit requires a high frequency oscillating circuit to charge or discharge the capacitor CP.